URLLoader remains open after close() is called

I have a Comet-based application in which GET requests remain open for 15 minutes at a time. When the user manually logs out, I call myURLLoader.close() on any active requests, but the requests are remaining open. Though they appear closed on the actionscript side, I have confirmed through Charles proxy and through monitoring on the server side that the requests are open under-the-hood.

The result of this is that if the user connects and disconnects a number of times in quick succession, he will reach the maximum number of concurrent requests for the application's process and any subsequent requests will fail.